Method and apparatus for controlling session

ABSTRACT

Provided are a method for controlling, by a multi-cell coordination entity (MCE), a session for transmitting a V2X message in a wireless communication system, and an apparatus for supporting the same. The method comprises the steps of: receiving, by the MCE, a cell ID and a multimedia broadcast multicast service (MBMS) service area identity (SAI) from a mobility management entity (MME); determining a multicast broadcast single frequency network (MBSFN) area to which the V2X message is to be transferred on the basis of the cell ID; transmitting a session control message to a base station which belongs to the determined MBSFN area, wherein the cell ID may be an ID of a cell to which the V2X message is transmitted.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system, andmore particularly, to a method of controlling a session for transmittinga V2X message on the basis of an MBMS system, and an apparatussupporting the method.

Related Art

3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) thatis an advancement of Universal Mobile Telecommunication System (UMTS) isbeing introduced with 3GPP release 8. In 3GPP LTE, orthogonal frequencydivision multiple access (OFDMA) is used for downlink, and singlecarrier-frequency division multiple access (SC-FDMA) is used for uplink.The 3GPP LTE adopts multiple input multiple output (MIMO) having maximumfour antennas. Recently, a discussion of 3GPP LTE-Advanced (LTE-A) whichis the evolution of the 3GPP LTE is in progress.

A Multimedia Broadcast/Multicast Service (MBMS) is a service ofsimultaneously transmitting a data packet to a plurality of users,similar to an existing Cell Broadcast Service (CBS). However, the CBS isa low-speed message-based service, while the MBMS is designed forhigh-speed multimedia data transmission. Further, the CBS is notInternet Protocol (IP)-based, whereas the MBMS is based on IP multicast.According to the MBMS, when users of a certain level are present in thesame cell, the users are allowed to receive the same multimedia datausing a shared resource (or channel), and thus the efficiency of radioresources may be improved and the users may use a multimedia service atlow costs.

The MBMS uses a shared channel so that a plurality of UEs efficientlyreceives data on one service. A BS allocates only one shared channel fordata on one service, instead of allocating as many dedicated channels asthe number of UEs to receive the service in one cell. The plurality ofUEs simultaneously receives the shared channel, thus improving theefficiency of radio resources. Regarding the MBMS, a UE may receive theMBMS after receiving system information on the cell.

An important communication technique such as public safety or groupcommunication system enablers for LTE (GCSE_LTE) has been introduced inRel-12. In Rel-12 GCSE, group communication has been designated aseMBMS. The eMBMS is designed to supply media content to a pre-plannedwide area (i.e., an MBSFN area). The MBSFN area is rather static (e.g.,configured by O&M), and cannot be dynamically adjusted according to userdistribution. Even if all radio resources of a frequency domain is notused, eMBMS transmission may occupy a full system bandwidth, andmultiplexing with unicast is not allowed in the same subframe. An MBSFNsubframe configuration is also rather static (e.g., configured by O&M).That is, an MBSFN subframe cannot be dynamically adjusted according tothe number of dynamic groups and a traffic load of a dynamic group.Therefore, when providing an importance communication service, a radioresource configuration for the eMBMS may be unnecessarily wasted.Therefore, single-cell point-to-multipoint (SCPTM) transmission isproposed for an effective use of the radio resource. While identifiablesignals are transmitted simultaneously in a plurality of cells in theMBSFN transmission, the MBMS service is transmitted in a single cell inthe SCPTM transmission.

There is a growing interest in a Device-to-Device (D2D) technology inwhich devices perform direct communication. In particular, D2D has beenin the spotlight as a communication technology for a public safetynetwork. A commercial communication network is rapidly changing to LTE,but the current public safety network is basically based on the 2Gtechnology in terms of a collision problem with existing communicationstandards and a cost. Such a technology gap and a need for improvedservices are leading to efforts to improve the public safety network.

The public safety network has higher service requirements (reliabilityand security) than the commercial communication network. In particular,if coverage of cellular communication is not affected or available, thepublic safety network also requires direct communication betweendevices, that is, D2D communication.

D2D communication may have various advantages in that it iscommunication between devices in proximity. For example, D2D UE has ahigh transfer rate and a low delay and may perform data communication.Furthermore, in D2D communication, traffic concentrated on a basestation can be distributed. If D2D UE plays the role of a relay, it mayalso play the role of extending coverage of a base station.

SUMMARY OF THE INVENTION

When a V2X message is transmitted based on the existing MBMS system, itmay be difficult to transfer the V2X message only for a specific area.For example, when the V2X message is transferred by using the existingMBMS system, it may be impossible to transfer the V2X message only to aspecific neighbor base station. Therefore, there is a need to newlypropose a method for limiting an area where the V2X message istransferred and an apparatus for supporting the method.

According to an embodiment, there is provided a method of controlling asession for transmitting a V2X message by a multi-cell coordinationentity (MCE) in a wireless communication system. The MCE may receive acell ID and a multimedia broadcast multicast service (MBMS) service areaidentity (SAI) from a mobility management entity (MME), determine amulticast broadcast single frequency network (MBSFN) area where the V2Xmessage is to be transferred on the basis of the cell ID, and transmit asession control message to a base station which belongs to thedetermined MBSFN area. The cell ID may be an ID of a cell in which theV2X message is transmitted.

The MBMS SAI may be set to 0.

The session control message may be an MBMS session start requestmessage. The cell ID and the MBMS SAI may be included in the MBMSsession start request message transmitted by the MME.

The session control message may be an MBMS session update requestmessage. The cell ID and the MBMS SAI may be included in the MBMSsession update request message transmitted by the MME.

The base station may be a road side unit (RSU).

According to another embodiment, there is provided a method ofcontrolling a session for transmitting a V2X message by an MCE in awireless communication system. The MCE may a session control messageincluding a cell list and a source cell indication from an MME, filterthe session control message on the basis of the cell list and the sourcecell indication, and transmit the filtered session control message to abase station. The source cell indication may indicate a cell in whichthe V2X message is transmitted.

The filtered session control message may include a list of cells managedby the base station.

The base station may be a base station which manages a cell indicated bythe source cell indication.

The base station may be a base station which manages a neighbor cell ofa cell indicated by the source cell indication.

The session control message may be any one of an MBMS session startrequest message and an MBMS session update request message.

The base station may be an RSU.

According to another embodiment, there is provided an MCE forcontrolling a session for transmitting a V2X message in a wirelesscommunication system. The MCE may include: a memory; a transceiver; anda processor for coupling the memory and the transceiver. The processormay be configured to: control the transceiver to receive a cell ID andan MBMS SAI from an MME; determine an MBSFN area where the V2X messageis to be transferred on the basis of the cell ID; and control thetransceiver to transmit a session control message to a base stationwhich belongs to the determined MBSFN area. The cell ID may be an ID ofa cell in which the V2X message is transmitted.

The MBMS SAI may be set to 0.

An area where a V2X message is transmitted can be limited.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a network architecture for an MBMS.

FIG. 3 shows a control plane and a user plane of a radio interfaceprotocol of an LTE system.

FIG. 4 shows a structure of an MBSFN subframe.

FIG. 5 shows an example of an MBSFN subframe configuration forperforming an MBMS service.

FIG. 6 shows a scenario considered for V2X.

FIG. 7 shows a method of transmitting a V2X message by using an MBMSsystem.

FIG. 8 is a drawing for explaining a procedure of transmitting a V2Xmessage according to an embodiment of the present invention.

FIG. 9A and FIG. 9B show a procedure of controlling a session fortransmitting a V2X message when an MCE does not filter the distributionof a session control message according to an embodiment of the presentinvention.

FIG. 10A and FIG. 10B show a procedure of controlling a session fortransmitting a V2X message when an MCE filters the distribution of asession control message according to an embodiment of the presentinvention.

FIG. 11A and FIG. 11B show a procedure of controlling a session fortransmitting a V2X message according to an embodiment of the presentinvention.

FIG. 12 is a block diagram showing a method in which an MCE controls asession for transmitting a V2X message according to an embodiment of thepresent invention.

FIG. 13 is a block diagram showing a method in which an MCE controls asession for transmitting a V2X message according to an embodiment of thepresent invention.

FIG. 14 is a block diagram illustrating a wireless communication systemaccording to the embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is evolved from IEEE 802.16e, and provides backwardcompatibility with a system based on the IEEE 802.16e. The UTRA is apart of a universal mobile telecommunication system (UMTS). 3rdgeneration partnership project (3GPP) long term evolution (LTE) is apart of an evolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses theOFDMA in a downlink and uses the SC-FDMA in an uplink. LTE-advanced(LTE-A) is an evolution of the LTE.

For clarity, the following description will focus on LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), a basetransceiver system (BTS), an access point, etc. One eNB 20 may bedeployed per cell. There are one or more cells within the coverage ofthe eNB 20. A single cell is configured to have one of bandwidthsselected from 1.25, 2.5, 5, 10, and 20 MHz, etc., and provides downlinkor uplink transmission services to several UEs. In this case, differentcells can be configured to provide different bandwidths.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) which is in chargeof control plane functions, and a system architecture evolution (SAE)gateway (S-GW) which is in charge of user plane functions. The MME/S-GW30 may be positioned at the end of the network and connected to anexternal network. The MME has UE access information or UE capabilityinformation, and such information may be primarily used in UE mobilitymanagement. The S-GW is a gateway of which an endpoint is an E-UTRAN.The MME/S-GW 30 provides an end point of a session and mobilitymanagement function for the UE 10. The EPC may further include a packetdata network (PDN) gateway (PDN-GW). The PDN-GW is a gateway of which anendpoint is a PDN.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, Inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), P-GW and S-GW selection,MME selection for handovers with MME change, serving GPRS support node(SGSN) selection for handovers to 2G or 3G 3GPP access networks,roaming, authentication, bearer management functions including dedicatedbearer establishment, support for public warning system (PWS) (whichincludes earthquake and tsunami warning system (ETWS) and commercialmobile alert system (CMAS)) message transmission. The S-GW host providesassorted functions including per-user based packet filtering (by e.g.,deep packet inspection), lawful interception, UE Internet protocol (IP)address allocation, transport level packet marking in the DL, UL and DLservice level charging, gating and rate enforcement, DL rate enforcementbased on APN-AMBR. For clarity MME/S-GW 30 will be referred to hereinsimply as a “gateway,” but it is understood that this entity includesboth the MME and S-GW.

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 and the eNB 20 are connected by means of a Uu interface. TheeNBs 20 are interconnected by means of an X2 interface. Neighboring eNBsmay have a meshed network structure that has the X2 interface. The eNBs20 are connected to the EPC by means of an S1 interface. The eNBs 20 areconnected to the MME by means of an S1-MME interface, and are connectedto the S-GW by means of S1-U interface. The S1 interface supports amany-to-many relation between the eNB 20 and the MME/S-GW.

The eNB 20 may perform functions of selection for gateway 30, routingtoward the gateway 30 during a radio resource control (RRC) activation,scheduling and transmitting of paging messages, scheduling andtransmitting of broadcast channel (BCH) information, dynamic allocationof resources to the UEs 10 in both UL and DL, configuration andprovisioning of eNB measurements, radio bearer control, radio admissioncontrol (RAC), and connection mobility control in LTE_ACTIVE state. Inthe EPC, and as noted above, gateway 30 may perform functions of pagingorigination, LTE_IDLE state management, ciphering of the user plane, SAEbearer control, and ciphering and integrity protection of NAS signaling.

FIG. 2 shows a network architecture for a Multimedia Broadcast/MulticastService (MBMS).

Referring to FIG. 2, the radio access network (EUTRAN) 200 includes amulti-cell coordination entity (hereinafter, “MCE”) 210 and a basestation (eNB) 220. The MCE 210 is a main entity for controlling the MBMSand plays a role to perform session management, radio resourceallocation or admission control of the base station 220. The MCE 210 maybe implemented in the base station 220 or may be implemented independentfrom the base station 220. The interface between the MCE 210 and thebase station 220 is called M2 interface. The M2 interface is an internalcontrol plane interface of the radio access network 200 and MBMS controlinformation is transmitted through the M2 interface. In case the MCE 210is implemented in the base station 220, the M2 interface may be presentonly logically.

The Evolved Packet Core (EPC) 250 includes an MME 260 and an MBMSgateway (GW) 270. The MBMS gateway 270 is an entity for transmittingMBMS service data and is positioned between the base station 220 and theBM-SC and performs MBMS packet transmission and broadcast to the basestation 220. The MBMS gateway 270 uses a PDCP and IP multicast totransmit user data to the base station 220 and performs session controlsignaling for the radio access network 200.

The interface between the MME 260 and the MCE 210 is a control planeinterface between the radio access network 200 and the EPC 250 and iscalled M3 interface. Control information related to MBMS session controlis transmitted through the M3 interface. The MME 260 and the MCE 210transmits, to the base station 220, session control signaling such as asession start/stop message for session start or session stop, and thebase station 220 may inform the UE through a cell notification that thecorresponding MBMS service has been started or stopped.

The interface between the base station 220 and the MBMS gateway 270 is auser plane interface and is called M1 interface.

FIG. 3 shows a control plane and a user plane of a radio interfaceprotocol of an LTE system. FIG. 3(a) shows a control plane of a radiointerface protocol of an LTE system. FIG. 3(b) shows a user plane of aradio interface protocol of an LTE system.

Layers of a radio interface protocol between the UE and the E-UTRAN maybe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. The radio interface protocol between the UE and the E-UTRAN maybe horizontally divided into a physical layer, a data link layer, and anetwork layer, and may be vertically divided into a control plane(C-plane) which is a protocol stack for control signal transmission anda user plane (U-plane) which is a protocol stack for data informationtransmission. The layers of the radio interface protocol exist in pairsat the UE and the E-UTRAN, and are in charge of data transmission of theUu interface.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel. A physical channel is mapped to the transport channel. Data istransferred between the MAC layer and the PHY layer through thetransport channel. Between different PHY layers, i.e., a PHY layer of atransmitter and a PHY layer of a receiver, data is transferred throughthe physical channel using radio resources. The physical channel ismodulated using an orthogonal frequency division multiplexing (OFDM)scheme, and utilizes time and frequency as a radio resource.

The PHY layer uses several physical control channels. A physicaldownlink control channel (PDCCH) reports to a UE about resourceallocation of a paging channel (PCH) and a downlink shared channel(DL-SCH), and hybrid automatic repeat request (HARQ) information relatedto the DL-SCH. The PDCCH may carry a UL grant for reporting to the UEabout resource allocation of UL transmission. A physical control formatindicator channel (PCFICH) reports the number of OFDM symbols used forPDCCHs to the UE, and is transmitted in every subframe. A physicalhybrid ARQ indicator channel (PHICH) carries an HARQ acknowledgement(ACK)/non-acknowledgement (NACK) signal in response to UL transmission.A physical uplink control channel (PUCCH) carries UL control informationsuch as HARQ ACK/NACK for DL transmission, scheduling request, and CQI.A physical uplink shared channel (PUSCH) carries a UL-uplink sharedchannel (SCH).

A physical channel consists of a plurality of subframes in time domainand a plurality of subcarriers in frequency domain. One subframeconsists of a plurality of symbols in the time domain. One subframeconsists of a plurality of resource blocks (RBs). One RB consists of aplurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use specific subcarriers of specific symbols of acorresponding subframe for a PDCCH. For example, a first symbol of thesubframe may be used for the PDCCH. The PDCCH carries dynamic allocatedresources, such as a physical resource block (PRB) and modulation andcoding scheme (MCS). A transmission time interval (TTI) which is a unittime for data transmission may be equal to a length of one subframe. Thelength of one subframe may be 1 ms.

The transport channel is classified into a common transport channel anda dedicated transport channel according to whether the channel is sharedor not. A DL transport channel for transmitting data from the network tothe UE includes a broadcast channel (BCH) for transmitting systeminformation, a paging channel (PCH) for transmitting a paging message, aDL-SCH for transmitting user traffic or control signals, etc. The DL-SCHsupports HARQ, dynamic link adaptation by varying the modulation, codingand transmit power, and both dynamic and semi-static resourceallocation. The DL-SCH also may enable broadcast in the entire cell andthe use of beamforming. The system information carries one or moresystem information blocks. All system information blocks may betransmitted with the same periodicity. Traffic or control signals of amultimedia broadcast/multicast service (MBMS) may be transmitted throughthe DL-SCH or a multicast channel (MCH).

A UL transport channel for transmitting data from the UE to the networkincludes a random access channel (RACH) for transmitting an initialcontrol message, a UL-SCH for transmitting user traffic or controlsignals, etc. The UL-SCH supports HARQ and dynamic link adaptation byvarying the transmit power and potentially modulation and coding. TheUL-SCH also may enable the use of beamforming. The RACH is normally usedfor initial access to a cell.

A MAC layer belongs to the L2. The MAC layer provides services to aradio link control (RLC) layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides a function ofmapping multiple logical channels to multiple transport channels. TheMAC layer also provides a function of logical channel multiplexing bymapping multiple logical channels to a single transport channel A MACsublayer provides data transfer services on logical channels.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer. The logicalchannels are located above the transport channel, and are mapped to thetransport channels.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting MBMS control information from the networkto a UE. The DCCH is a point-to-point bi-directional channel used by UEshaving an RRC connection that transmits dedicated control informationbetween a UE and the network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink. The MTCH isa point-to-multipoint downlink channel for transmitting traffic datafrom the network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RLC layer belongs to the L2. The RLC layer provides a function ofadjusting a size of data, so as to be suitable for a lower layer totransmit the data, by concatenating and segmenting the data receivedfrom an upper layer in a radio section. In addition, to ensure a varietyof quality of service (QoS) required by a radio bearer (RB), the RLClayer provides three operation modes, i.e., a transparent mode (TM), anunacknowledged mode (UM), and an acknowledged mode (AM). The AM RLCprovides a retransmission function through an automatic repeat request(ARQ) for reliable data transmission. Meanwhile, a function of the RLClayer may be implemented with a functional block inside the MAC layer.In this case, the RLC layer may not exist.

A packet data convergence protocol (PDCP) layer belongs to the L2. ThePDCP layer provides a function of header compression function thatreduces unnecessary control information such that data being transmittedby employing IP packets, such as IPv4 or IPv6, can be efficientlytransmitted over a radio interface that has a relatively smallbandwidth. The header compression increases transmission efficiency inthe radio section by transmitting only necessary information in a headerof the data. In addition, the PDCP layer provides a function ofsecurity. The function of security includes ciphering which preventsinspection of third parties, and integrity protection which preventsdata manipulation of third parties.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer takes a role of controlling a radioresource between the UE and the network. For this, the UE and thenetwork exchange an RRC message through the RRC layer. The RRC layercontrols logical channels, transport channels, and physical channels inrelation to the configuration, reconfiguration, and release of RBs. AnRB is a logical path provided by the L1 and L2 for data delivery betweenthe UE and the network. That is, the RB signifies a service provided theL2 for data transmission between the UE and E-UTRAN. The configurationof the RB implies a process for specifying a radio protocol layer andchannel properties to provide a particular service and for determiningrespective detailed parameters and operations. The RB is classified intotwo types, i.e., a signaling RB (SRB) and a data RB (DRB). The SRB isused as a path for transmitting an RRC message in the control plane. TheDRB is used as a path for transmitting user data in the user plane.

A Non-Access Stratum (NAS) layer placed over the RRC layer performsfunctions, such as session management and mobility management.

Referring to FIG. 3(a), the RLC and MAC layers (terminated in the eNB onthe network side) may perform functions such as scheduling, automaticrepeat request (ARQ), and hybrid automatic repeat request (HARQ). TheRRC layer (terminated in the eNB on the network side) may performfunctions such as broadcasting, paging, RRC connection management, RBcontrol, mobility functions, and UE measurement reporting andcontrolling. The NAS control protocol (terminated in the MME of gatewayon the network side) may perform functions such as a SAE bearermanagement, authentication, LTE_IDLE mobility handling, pagingorigination in LTE_IDLE, and security control for the signaling betweenthe gateway and UE.

Referring to FIG. 3(b), the RLC and MAC layers (terminated in the eNB onthe network side) may perform the same functions for the control plane.The PDCP layer (terminated in the eNB on the network side) may performthe user plane functions such as header compression, integrityprotection, and ciphering.

Hereinafter, an RRC State of a UE and RRC Connection Procedure areDescribed.

An RRC state indicates whether an RRC layer of the UE is logicallyconnected to an RRC layer of the E-UTRAN. The RRC state may be dividedinto two different states such as an RRC connected state and an RRC idlestate. When an RRC connection is established between the RRC layer ofthe UE and the RRC layer of the E-UTRAN, the UE is in RRC_CONNECTED, andotherwise the UE is in RRC_IDLE. Since the UE in RRC_CONNECTED has theRRC connection established with the E-UTRAN, the E-UTRAN may recognizethe existence of the UE in RRC_CONNECTED and may effectively control theUE. Meanwhile, the UE in RRC_IDLE may not be recognized by the E-UTRAN,and a CN manages the UE in unit of a TA which is a larger area than acell. That is, only the existence of the UE in RRC_IDLE is recognized inunit of a large area, and the UE must transition to RRC_CONNECTED toreceive a typical mobile communication service such as voice or datacommunication.

In RRC_IDLE state, the UE may receive broadcasts of system informationand paging information while the UE specifies a discontinuous reception(DRX) configured by NAS, and the UE has been allocated an identification(ID) which uniquely identifies the UE in a tracking area and may performpublic land mobile network (PLMN) selection and cell reselection. Also,in RRC_IDLE state, no RRC context is stored in the eNB.

In RRC_CONNECTED state, the UE has an E-UTRAN RRC connection and acontext in the E-UTRAN, such that transmitting and/or receiving datato/from the eNB becomes possible. Also, the UE can report channelquality information and feedback information to the eNB. InRRC_CONNECTED state, the E-UTRAN knows the cell to which the UE belongs.Therefore, the network can transmit and/or receive data to/from UE, thenetwork can control mobility (handover and inter-radio accesstechnologies (RAT) cell change order to GSM EDGE radio access network(GERAN) with network assisted cell change (NACC)) of the UE, and thenetwork can perform cell measurements for a neighboring cell.

In RRC_IDLE state, the UE specifies the paging DRX cycle. Specifically,the UE monitors a paging signal at a specific paging occasion of everyUE specific paging DRX cycle. The paging occasion is a time intervalduring which a paging signal is transmitted. The UE has its own pagingoccasion.

A paging message is transmitted over all cells belonging to the sametracking area. If the UE moves from one TA to another TA, the UE willsend a tracking area update (TAU) message to the network to update itslocation.

When the user initially powers on the UE, the UE first searches for aproper cell and then remains in RRC_IDLE in the cell. When there is aneed to establish an RRC connection, the UE which remains in RRC_IDLEestablishes the RRC connection with the RRC of the E-UTRAN through anRRC connection procedure and then may transition to RRC_CONNECTED. TheUE which remains in RRC_IDLE may need to establish the RRC connectionwith the E-UTRAN when uplink data transmission is necessary due to auser's call attempt or the like or when there is a need to transmit aresponse message upon receiving a paging message from the E-UTRAN.

To manage mobility of the UE in the NAS layer, two states are defined,i.e., an EPS mobility management-REGISTERED (EMM-REGISTERED) state andan EMM-DEREGISTERED state. These two states apply to the UE and the MME.Initially, the UE is in the EMM-DEREGISTERED state. To access a network,the UE performs a process of registering to the network through aninitial attach procedure. If the attach procedure is successfullyperformed, the UE and the MME enter the EMM-REGISTERED state.

To manage a signaling connection between the UE and the EPC, two statesare defined, i.e., an EPS connection management (ECM)-IDLE state and anECM-CONNECTED state. These two states apply to the UE and the MME. Whenthe UE in the ECM-IDLE state establishes an RRC connection with theE-UTRAN, the UE enters the ECM-CONNECTED state. When the MME in theECM-IDLE state establishes an S1 connection with the E-UTRAN, the MMEenters the ECM-CONNECTED state. When the UE is in the ECM-IDLE state,the E-UTRAN does not have context information of the UE. Therefore, theUE in the ECM-IDLE state performs a UE-based mobility related proceduresuch as cell selection or reselection without having to receive acommand of the network. On the other hand, when the UE is in theECM-CONNECTED state, mobility of the UE is managed by the command of thenetwork. If a location of the UE in the ECM-IDLE state becomes differentfrom a location known to the network, the UE reports the location of theUE to the network through a tracking area update procedure.

Hereinafter, an MBMS and a Multicast/Broadcast Single Frequency Network(MBSFN) are Described.

MBSFN transmission or MBSFN-mode transmission refers to a simultaneoustransmission scheme in which a plurality of cells transmits the samesignal at the same time. MBSFN transmissions from a plurality of cellswithin an MBSFN area are perceived as a single transmission for a UE.

The MBMS service may be managed or localized in a cell-based orgeography-based manner. An area in which a specific MBMS service isprovided is widely referred to as an MBMS service area. For example, ifan area in which a specific MBSMS service A proceeds is an MBMS servicearea A, a network in the MBMS service area A may be in a state oftransmitting the MBMS service A. In this case, the UE may receive theMBMS service A according to a UE capability. The MBMS service area maybe defined in terms of an application and a service as to whether aspecific service is provided in a specific area.

A transport channel for the MBMS, that is, a multicast channel (MCH),may be mapped to a logical channel, e.g., a multicast control channel(MCCH) or a multicast traffic channel (MTCH). The MCCH transmits anMBMS-related RRC message, and the MTCH transmits a traffic of a specificMBMS service. One MCCH exists in every one MBMS single frequency network(MBSFN) region for transmitting the same MBMS information/traffic. TheMCCH includes one MBSFN region configuration RRC message, and has a listof all MBMS services. If the MBMS-related RRC message is changed in aspecific MCCH, a physical downlink control channel (PDCCH) transmits anMBMS radio network temporary identity (M-RNTI) and an indication forindicating the specific MCCH. The UE which supports the MBMS may receivethe M-RNTI and the MCCH indication through the PDCCH, may recognize thatthe MBMS-related RRC message is changed in the specific MCCH, and mayreceive the specific MCCH. The RRC message of the MCCH may be changed inevery modification period, and is broadcast repetitively in everyrepetition period. A notification mechanism is used to inform an MCCHchange caused by a presence of an MCCH session start or MBMS countingrequest message. The UE detects the MCCH change informed without havingto depend on the notification mechanism through MCCH monitoring in themodification period. The MTCH is a logical channel on which an MBMSservice carried. If many services are provided in an MBSFN region, aplurality of MTCHs may be configured.

A UE may also be provided with a dedicated service while being providedwith an MBMS service. For example, a user may chat on the user's ownsmartphone using an instant messaging (IM) service, such as MSN orSkype, simultaneously with watching a TV on the smartphone through anMBMS service. In this case, the MBMS service is provided through an MTCHreceived by a plurality of UEs at the same time, while a serviceprovided for each individual UE, such as the IM service, is providedthrough a dedicated bearer, such as a dedicated control channel (DCCH)or dedicated traffic channel (DTCH).

In one area, a BS may use a plurality of frequencies at the same time.In this case, in order to efficiently use radio resources, a network mayselect one of the frequencies to provide an MBMS service only in thefrequency and may provide a dedicated bearer for each UE in allfrequencies. In this case, when a UE, which has been provided with aservice using a dedicated bearer in a frequency where no MBMS service isprovided, wishes to be provided with an MBMS service, the UE needs to behanded over to an MBMS providing frequency. To this end, the UEtransmits an MBMS interest indication to a BS. That is, when the UEwishes to receive an MBMS service, the UE transmits an MBMS interestindication to the BS. When the BS receives the indication, the BSrecognizes that the UE wishes to receive the MBMS service and hands theUE over to an MBMS providing frequency. Here, the MBMS interestindication is information indicating that the UE wishes to receive anMBMS service, which additionally includes information on a frequency towhich the UE wishes to be handed over.

The UE, which wishes to receive a specific MBMS service, firstidentifies information on a frequency at which the specific service isprovided and information on broadcast time at which the specific serviceis provided. When the MBMS service is already on air or is about to beon air, the UE assigns the highest priority to the frequency at whichthe MBMS service is provided. The UE performs a cell reselectionprocedure using reset frequency priority information and moves to a cellproviding the MBMS service to receive the MBMS service.

When the UE is receiving an MBMS service or is interested in receivingan MBMS service and when the UE is allowed to receive an MBMS servicewhile camping on an MBMS service-providing frequency, it may beconsidered that the frequency is assigned the highest priority during anMBMS session as long as the following situations last while thereselected cell is broadcasting SIB13.

-   -   When SIB15 of a serving cell indicates that one or more MBMS        service area identities (SAIs) are included in the user service        description (USD) of the service.    -   SIB15 is not broadcast in a serving cell, and the frequency is        included in the USD of the service.

A UE needs to be able to receive an MBMS in RRC_IDLE and RRC_CONNECTEDstates.

FIG. 4 shows a structure of an MBSFN subframe.

Referring to FIG. 4, MBSFN transmission is configured by the subframe. Asubframe configured to perform MBSFN transmission is referred to as anMBSFN subframe. In a subframe configured as an MBSFN subframe, MBSFNtransmission is performed in OFDM symbols other than first two OFDMsymbols for PDCH transmission. For convenience, a region used for MBSFNtransmission is defined as an MBSFN region. In the MBSFN region, no CRSfor unicast is transmitted but an MBMS-dedicated RS common to all cellsparticipating in transmission is used.

In order to notify even a UE receiving no MBMS that no CRS istransmitted in the MBSFN region, system information on a cell isbroadcast including configuration information on the MBSSFN subframe.Since most UEs perform radio resource management (RRM), radio linkfailure (RLF) processing, and synchronization using a CRS, it isimportant to indicate the absence of a CRS in a specific region. A CRSis transmitted in first two OFDM symbols used as a PDCCH in the MBSFNsubframe, and this CRS is not for an MBSFN. A CP of the CRS transmittedin the first two OFDM symbols used as the PDCCH in the MBSFN subframe(that is, whether the CRS uses a normal CP or an extended CP) follows aCP applied to a normal subframe, that is, a subframe which is not anMBSFN subframe. For example, when a normal subframe 411 uses a normalCP, a CRS according to the normal CP is also used in the first two OFDMsymbols 412 of the MBSFN subframe.

Meanwhile, a subframe to be configured as an MBSFN subframe isdesignated by FDD and TDD, and a bitmap is used to indicate whether asubframe is an MBSFN subframe. That is, when a bit corresponding to aspecific subframe in a bitmap is 1, it is indicated that the specificsubframe is configured as an MBSFN subframe.

FIG. 5 shows an example of an MBSFN subframe configuration forperforming an MBMS service.

Referring to FIG. 5, a UE acquires MBSFN subframe configurationinformation, MBSFN notification configuration information, and MBSFNarea information list to perform the MBMS service.

The UE may know the MBSFN subframe configuration information, that is, aposition of an MBSFN subframe, through SIB2 and RRC dedicated signaling.For example, the MBSFN subframe configuration information may beincluded in an MBSFN-SubframeConfig information element (IE).

In addition, the UE may acquire the MBSFN area information list and theMBMS notification configuration information as information required toacquire MBMS control information related to one or more MBSFN regions inwhich the MBMS service can be performed through SIB13. Herein, for eachMBSFN region, the MB SFN area information list may include an MBSFNregion ID, information regarding an MBSFN region in an MBSFN subframe ina corresponding MBSFN region, information such as an MBSFN subframeposition at which transmission of an MCCH occurs as an MBMS controlinformation channel, or the like. For example, the MBSFN areainformation list may be included in an MBSFN-AreaInfoList informationelement. Meanwhile, the MBSFN notification configuration information isconfiguration information for a subframe position at which an MBMSnotification occurs to inform that there is a change in the MBSFN regionconfiguration information. For example, the MBSFN notificationconfiguration information may be included in an MBMS-NotificationConfiginformation element. The MBSFN notification configuration informationincludes time information utilized to notify an MCCH change applicableto all MBSFN regions. For example, the time information may include anotification repetition coefficient (notificationRepetitionCoeff), anotification offset (notificationOffset), and a notification subframeindex (notificationSF-Index). Herein, the notification repetitioncoefficient implies a common notification repetition period for allMCCHs. The notification offset indicates an offset of a radio frame inwhich the MCCH change notification information is scheduled. Inaddition, the notification subframe index is a subframe index used totransmit an MCCH change notification on a PDCCH.

The UE may acquire the MBSFN region configuration information through anMCCH corresponding to each of the MBSFN regions acquired through SIB13.The MBSFN region configuration information may be included in anMBSFNAreaconfiguration message, and contains information regardingphysical multicast channels (PMCHs) used in a corresponding MBSFNregion. For example, information regarding each PMCH may include aposition of an MBSFN subframe in which a corresponding PMCH is located,modulation and coding scheme (MCS) level information used for datatransmission in a corresponding subframe, MBMS service informationtransmitted by the corresponding PMCH, or the like.

The UE receives MCH data through the MTCH on the basis of the PMCH.Scheduling on a time for the MCH data may be known through MCHscheduling information (MSI) delivered through the PMCH. The MSIcontains information regarding how long corresponding MCH datatransmission is continued.

Hereinafter, Single-Cell Point-to-Multipoint (SCPTM) Transmission isDescribed.

A transmission method of an MBMS service includes SCPTM transmission andmultimedia broadcast multicast service single frequency network (MBSFN)transmission. While identifiable signals are transmitted simultaneouslyin a plurality of cells in the MBSFN transmission, the MBMS service istransmitted in a single cell in the SCPTM transmission. Therefore,unlike in the MBSFN transmission, synchronization between cells is notnecessary in the SCPTM transmission. Further, the SCPTM transmissiondirectly uses the existing PDSCH, and thus has a unicast feature unlikein the MBSFN transmission. That is, a plurality of UEs read the samePDCCH, and acquire an RNTI for each service to receive an SCPTM service.An SCPTM-dedicated MCCH is introduced, and if it is determined that aservice desired by the UE is an SCPTM service through the MCCH, the UEmay acquire a corresponding RNTI value and read a PDCCH through acorresponding RNTI to receive the SCPTM service.

Hereinafter, V2X Will be Described.

V2X communication implies a communication scheme which exchanges orshares information such as a traffic condition or the like whilecommunicating with a road infrastructure and other vehicles duringdriving. V2X may include a vehicle to vehicle (V2V) which meanscommunication between vehicles, a vehicle to pedestrian (V2P) whichmeans communication between a vehicle and a UE carried by an individual,and a vehicle to infrastructure (V2I)/network (N) which meanscommunication between a vehicle and a roadside unit (RSU)/network. Inthis case, the RSU may be a transportation infrastructure entityimplemented by an eNB (or eNodeB-type RSU) or a stationary UE (orUE-type RSU).

FIG. 6 shows a scenario considered for V2X.

Referring to FIG. 6(a), a scenario supporting only a V2V operation basedon only PC5 which is an interface between UEs may be considered for V2X.Referring to FIG. 6(b), a scenario supporting only a V2V operation basedon only Uu which is an interface between an eNB and a UE may beconsidered for V2X. Referring to FIG. 6(c), a scenario supporting a V2Voperation based on both PC5 and Uu may be considered for V2X.

FIG. 7 shows a method of transmitting a V2X message by using an MBMSsystem.

Referring to FIG. 7, in order to transfer the V2X message to an area ofmore than one eNB and/or more than one RSU, the existing MBMS system maybe considered. It is assumed that an eNB2 and an eNB3 are neighbors ofthe eNB1. On the other hand, it is assumed that an eNB4 is not aneighbor of the eNB1. When a vehicle transmits a V2X related message viaa Uu interface to the eNB1, this message should be provided not to theeNB4 but to the eNB2 and the eNB3. However, when the V2X message istransmitted based on the current MBMS system, the V2X messagetransmitted from the eNB1 cannot be transferred only to the eNB2 and theeNB3 by excluding the eNB4. Therefore, there is a need to propose aprocedure for transferring the V2X message only in a narrow area withrespect to an eNB which receives the V2X message.

Hereinafter, a method of transmitting a V2X message is describedaccording to an embodiment of the present invention.

In the present specification, an eNB may be a concept that includes notonly a typical eNB but also an RSU. The RSU may be an eNB-type RSU or aUE-type RSU.

FIG. 8 is a drawing for explaining a procedure of transmitting a V2Xmessage according to an embodiment of the present invention.

Referring to FIG. 8, it is assumed that an eNB1 manages cells 1, 2, and3, an eNB2 manages cells 4, 5, and 6, and an eNB3 manages cells 7, 8,and 9. It is assumed that the eNBs 1, 2, and 3 are connected with thesame MCE via an M2 interface. It is assumed that the MCE is connectedwith an MME via an M3 interface. It is assumed that an accident such asa vehicle collision occurs in an area of the cell 3.

Hereinafter, a V2X message transmission method based on an SCPTMoperation (first method) and a V2X message transmission method based onan MBMS operation (second method) will be described according to anembodiment of the present invention.

<First Method>

The first method is based on SCPTM operation. A V2X server may indicatea list of cells, which need to transmit the V2X message, and informationrelated to a cell which receives the V2X message. The informationrelated to the cell which receives the V2X message may be informationrelated to a cell which receives the V2X message from a vehicle.Accordingly, an area where the V2X message to be broadcast can belimited.

The first method may be classified again according to whether an MCEfilters the distribution of a session control message. For example, thesession control message may be any one of an MBMS session start requestmessage and an MBMS session update request message.

FIG. 9A and FIG. 9B show a procedure of controlling a session fortransmitting a V2X message when an MCE does not filter the distributionof a session control message according to an embodiment of the presentinvention.

Referring to FIG. 9A, in step S900, an eNB1 may transmit to a V2X servera V2X message received from a vehicle within the coverage of the eNB1.The V2X message may contain information on an accident event. The V2Xserver may obtain a cell ID through the V2X message. Alternatively, theV2X server may obtain the cell ID through reporting by the vehicle. Inthe embodiment of FIG. 8, the eNB1 may transmit to the V2X server a V2Xmessage received from a vehicle within the coverage of a cell 3. The V2Xserver may obtain a cell ID of the cell 3 through the V2X message orreporting by the vehicle.

In step S910, the V2X server may make a list of cells which need totransmit the V2X message. The cell list may include a cell whichtransmits the V2X message. In the embodiment of FIG. 8, the list ofcells which need to transmit the V2X message may include cells 1 to 9.The list of cells which need transmit the V2X message may include a cell(i.e., the cell 3) which transmits the V2X message.

In step S920, the V2X may transmit to a BM-SC an MBMS session startinitiate message, an MBMS session update initiate message, an existingmessage, a new IE included in the existing message, or a new IE includedin the new message. The message may include a cell list and a sourcecell indication. The source cell indication may indicate informationrelated to the cell which transmits the V2X message. The source cellindication may indicate whether each cell within the cell list transmitsthe V2X message. Alternatively, the source cell indication may be an IDof the cell which transmits the V2X message. In the embodiment of FIG.8, the cell list may include the cells 1 to 9. The source cellindication may be an indication for the cell 3. Alternatively, thesource cell indication may be an ID of the cell 3.

In step S930, upon receipt of the MBMS session start initiate messagefrom the V2X server, the BM-SC may transmit an MBMS session start/updaterequest message to an MBMS GW. The MBMS session start request messagemay include a cell list and a source cell indication. Alternatively,upon receipt of the MBMS session update initiate message from the V2Xserver, the BM-SC may transmit an MBMS session update request message tothe MBMS GW. The MBMS session update request message may include thecell list and the source cell indication.

In step S940, the MBMS GW may transmit the MBMS session start requestmessage to an MME. The MBMS session start request message may includethe cell list and the source cell indication. Alternatively, the MBMSmay transmit the MBMS session update request message to the MME. TheMBMS session update request message may include the cell list and thesource cell indication.

Referring to FIG. 9B, in step S950, the MME may transmit the MBMSsession start request message to an MCE. The MBMS session start requestmessage may include the cell list and the source cell indication.Alternatively, the MME may transmit the MBMS session update requestmessage to the MCE. The MBMS session update request message may includethe cell list and the source cell indication.

In step S960, upon receipt of the MBMS session start request messagefrom the MME, the MCE may transmit the MBMS session start requestmessage to an eNB. The MBMS session start request message may includethe cell list and the source cell indication. Alternatively, uponreceipt of the MBMS session update request message from the MME, the MCEmay transmit the MBMS session update request message to the eNB. TheMBMS session update request message may include the cell list and thesource cell indication. The cell list may be identical to a cell listreceived from the MME. That is, the MCE may transmit the cell listreceived from the MME directly to the eNB. The eNB may be an eNB managedby the MCE. In the embodiment of FIG. 8, since the cell list received bythe MCE from the MME includes the cells 1 to 9, the cell listtransmitted by the MCE to the eNBs 1 to 3 may include the cells 1 to 9.In addition, the source cell indication may indicate the cell 3.

In step S970, upon receipt of the MBMS session start request message orthe MBMS session update request message from the MCE, the eNB may checkthe cell list and the source cell indication.

If the cell managed by the eNB is contained in the cell list and the eNBis an eNB for managing a cell indicated by the source cell indication,the eNB may broadcast the V2X message. Alternatively, if the cellmanaged by the eNB is contained in the cell list and the eNB is an eNBhaving the cell indicated by the source cell indication as a neighbor,the eNB may broadcast the V2X message. The eNB may broadcast the V2Xmessage only in a cell within the cell list. Alternatively, the eNB maybroadcast the V2X message in all cells controlled by the eNB. Inaddition, the eNB may transmit an MBMS session start response message tothe MCE in response to the MBMS session start request message.Alternatively, the eNB may transmit an MBMS session update responsemessage to the MCE in response to the MBMS session update requestmessage.

If the cell managed by the eNB is contained in the cell list but the eNBis not the eNB for managing the cell indicated by the source cellindication and the eNB is not the eNB having the cell indicated by thesource cell indication as the neighbor cell, the eNB may not broadcastthe V2X message. In addition, the eNB may reject or ignore the MBMSsession start request message and the MBMS session update requestmessage.

In the embodiment of FIG. 8, the eNB1 may check the cell list includingthe cells 1 to 9 and the source cell indication indicating the cell 3.Since the cells 1 to 3 managed by the eNB1 are contained in the celllist and the eNB1 is the eNB for managing the cell 3 indicated by thesource cell indication, the eNB1 may broadcast the V2X message.Thereafter, the eNB1 may transmit the MBMS session start responsemessage or the MBMS session update response message to the MCE.

In the embodiment of FIG. 8, the eNB2 may check the cell list includingthe cells 1 to 9 and the source cell indication indicating the cell 3.Since the cells 4 to 6 managed by the eNB2 are contained in the celllist and the eNB2 is the eNB for managing the cell 3 indicated by thesource cell indication, the eNB2 may broadcast the V2X message.Thereafter, the eNB2 may transmit the MBMS session start responsemessage or the MBMS session update response message to the MCE.

In the embodiment of FIG. 8, the eNB3 may check the cell list includingthe cells 1 to 9 and the source cell indication indicating the cell 3.Since the cells 7 to 9 managed by the eNB3 are contained in the celllist but the eNB3 is not the eNB for managing the cell 3 indicated bythe source cell indication and the eNB3 is not the eNB having the cell 3indicated by the source cell indication as the neighbor cell, the eNB3may not broadcast the V2X message. Thereafter, the eNB3 may reject orignore the MBMS session start response message or the MBMS sessionupdate response message.

FIG. 10A and FIG. 10B show a procedure of controlling a session fortransmitting a V2X message when an MCE filters the distribution of asession control message according to an embodiment of the presentinvention.

Referring to FIG. 10A, in step S1000, an eNB1 may transmit to a V2Xserver a V2X message received from a vehicle within the coverage of theeNB1. The V2X message may contain information on an accident event. TheV2X server may obtain a cell ID through the V2X message. Alternatively,the V2X server may obtain the cell ID through reporting by the vehicle.In the embodiment of FIG. 8, the eNB1 may transmit to the V2X server aV2X message received from a vehicle within the coverage of a cell 3. TheV2X server may obtain a cell ID of the cell 3 through the V2X message orreporting by the vehicle.

In step S1010, the V2X server may make a list of cells which need totransmit the V2X message. The cell list may include a cell whichtransmits the V2X message. In the embodiment of FIG. 8, the list ofcells which need to transmit the V2X message may include cells 1 to 9.The list of cells which need transmit the V2X message may include a cell(i.e., the cell 3) which transmits the V2X message.

In step S1020, the V2X may transmit to a BM-SC an MBMS session startinitiate message, an MBMS session update initiate message, an existingmessage, a new IE included in the existing message, or a new IE includedin the new message. The message may include a cell list and a sourcecell indication. The source cell indication may indicate informationrelated to the cell which transmits the V2X message. When each celltransmits the V2X message, the source cell indication may be anindication for each of the cells within a cell list for indicating eachof the cells. Alternatively, the source cell indication may be an ID ofthe cell which transmits the V2X message. In the embodiment of FIG. 8,the cell list may include the cells 1 to 9. The source cell indicationmay be an indication for the cell 3. Alternatively, the source cellindication may be an ID of the cell 3.

In step S1030, upon receipt of the MBMS session start initiate messagefrom the V2X server, the BM-SC may transmit an MBMS session start/updaterequest message to an MBMS GW. The MBMS session start request messagemay include a cell list and a source cell indication. Alternatively,upon receipt of the MBMS session update initiate message from the V2Xserver, the BM-SC may transmit an MBMS session update request message tothe MBMS GW. The MBMS session update request message may include thecell list and the source cell indication.

In step S1040, the MBMS GW may transmit the MBMS session start requestmessage to an MME. The MBMS session start request message may includethe cell list and the source cell indication. Alternatively, the MBMSmay transmit the MBMS session update request message to the MME. TheMBMS session update request message may include the cell list and thesource cell indication.

Referring to FIG. 10B, in step S1050, the MME may transmit the MBMSsession start request message to an MCE. The MBMS session start requestmessage may include the cell list and the source cell indication.Alternatively, the MME may transmit the MBMS session update requestmessage to the MCE. The MBMS session update request message may includethe cell list and the source cell indication.

In step S1060, upon receipt of the MBMS session start request messagefrom the MME, the MCE may filter the distribution of the MBMS sessionstart request message on the basis of the cell list and the source cellindication. Alternatively, upon receipt of the MBMS session updaterequest message from the MME, the MCE may filter the distribution of theMBMS session update request message on the basis of the cell list andthe source cell indication. Unlike in the embodiment of FIG. 9B, the MCEmay filter the MBMS session start request message or MBMS session updaterequest message, which is received from the MME, and transmit it to theeNB for managing the cell indicated by the source cell indication.

In step S1070, if a specific eNB is the eNB for managing the cellindicated by the source cell indication, the MCE may transmit the MBMSsession start request message or the MBMS session update request messageto the specific eNB. Alternatively, if the specific eNB is the eNBhaving the cell indicated by the source cell indication as the neighborcell, the MCE may transmit the MBMS session start request message or theMBMS session update request message to the specific eNB. The MBMSsession start request message or the MBMS session update request messagemay include a cell list consisting of cells controlled by the specificeNB. If the specific eNB is not the eNB for managing the cell indicatedby the source cell identification and the specific eNB is not the eNBhaving the cell indicated by the source cell indication as the neighborcell, the MCE may not transmit any message to the specific eNB.

In the embodiment of FIG. 8, since the eNB1 is the eNB for managing thecell 3 indicated by the source cell indication, the MCE may transmit theMBMS session start request message or the MBMS session update requestmessage to the eNB1. The MBMS session start request message or the MBMSsession update request message may include the cell list including thecells 1 to 3 and the source cell indication indicating the cell 3.

In the embodiment of FIG. 8, since the eNB2 is the eNB having the cell 3indicated by the source cell indication as the neighbor cell, the MCEmay transmit the MBMS session start request message or the MBMS sessionupdate request message to the eNB2. The MBMS session start requestmessage or the MBMS session update request message may include the celllist including the cells 4 to 6 and the source cell indicationindicating the cell 3.

In the embodiment 8, since the eNB3 is not the eNB for managing the cell3 indicated by the source cell indication and the eNB3 is not the eNBhaving the cell 3 indicated by the source cell indication as theneighbor cell, the MCE may not transmit any message to the eNB3.

In step S1080, if the eNB receives the MBMS session start requestmessage or the MBMS session update request message, the eNB maybroadcast the V2X message. The eNB may broadcast the V2X message only ina cell within the cell list. Alternatively, the eNB may broadcast theV2X message in all cells controlled by the eNB. In addition, the eNB maytransmit an MBMS session start response message to the MCE in responseto the MBMS session start request message. Alternatively, the eNB maytransmit an MBMS session update response message to the MCE in responseto the MBMS session update request message.

In the embodiment of FIG. 8, the eNB1 and the eNB2 which have receivedthe MBMS session start request message or the MBMS session updaterequest message may broadcast the V2X message. On the other hand, theeNB3 which has not received the MBMS session start request message andthe MBMS session update request message may not broadcast the V2Xmessage.

According to the first method proposed in FIG. 9A to FIG. 10B, the V2Xmessage may be broadcast only in a neighbor eNB.

<Second Method>

The second method is based on an MBMS operation. A V2X server mayindicate an ID of a cell, which transmits a V2X message, to an MCE. AnMBMS service area identity (SAI) may have a value 0. Accordingly, anarea where the V2X message needs to be broadcast can be limited.

FIG. 11A and FIG. 11B show a procedure of controlling a session fortransmitting a V2X message according to an embodiment of the presentinvention.

Referring to FIG. 11A, in step S1100, an eNB1 may transmit to a V2Xserver a V2X message received from a vehicle within the coverage of theeNB1. The V2X message may contain information on an accident event. TheV2X server may obtain a cell ID through the V2X message. Alternatively,the V2X server may obtain the cell ID through reporting by the vehicle.

In step S1110, the V2X server may recognize the cell which transmits theV2X message.

In step S1120, the V2X may transmit to a BM-SC an MBMS session startinitiate message, an MBMS session update initiate message, an existingmessage, a new IE included in the existing message, or a new IE includedin the new message. The message may include the cell ID of the cell fortransmitting the V2X message.

In step S1130, upon receipt of the message from the V2X server, if themessage includes the cell ID indicating the cell for transmitting theV2X message, the BM-SC may set an MBMS SAI value to 0.

In step S1140, the BM-SC may transmit an MBMS session start requestmessage or an MBMS session update request message to an MBMS GW. TheMBMS session start request message or the MBMS session update requestmessage may include a cell ID received from the V2X server and the MBMSSAI with the value 0.

In step S1150, the MBMS GW may transmit the MBMS session start requestmessage or the MBMS session update request message to an MME. The MBMSsession start request message or the MBMS session update request messagemay include a cell ID received from the BM-SC and the MBMS SAI with thevalue 0.

Referring to FIG. 11B, in step S1160, the MME may transmit the MBMSsession start request message or the MBMS session update request messageto the MCE. The MBMS session start request message or the MBMS sessionupdate request message may include the cell ID received from the MBMS GWand the MBMS SAI with a value 0.

In step S1170, if the MCE receives the MBMS session start requestmessage or the MBMS session update request message from the MME, the MCEmay determine an MBSFN area where a service should be transferred basedon the cell ID received from the MME. This is because the MBMS SAI has avalue 0. This operation may reduce a size of the MBSFN area where theV2X message needs to be transferred.

In step S1180, the MCE may transmit the MBMS session start requestmessage or the MBMS session update request message to the eNB. The eNBmay be an eNB belonging to a newly determined MBSFN area.

In step S1190, upon receipt of the MBMS session start request message orthe MBMS session update request message, the eNB may broadcast the V2Xmessage received from the MBMS GW.

According to the second method proposed in FIG. 11A and FIG. 11B, thearea where the V2X message is transferred may be decreased.

FIG. 12 is a block diagram showing a method in which an MCE controls asession for transmitting a V2X message according to an embodiment of thepresent invention.

Referring to FIG. 12, in step S1210, the MCE may receive a cell ID and amultimedia broadcast multicast service (MBMS) service area identity(SAI) from a mobility management entity (MME). The cell ID may be an IDof a cell in which the V2X message is transmitted. The MBMS SAI may beset to 0.

In step S1220, the MCE may determine a multicast broadcast singlefrequency network (MBSFN) area where the V2X message is to betransferred based on the cell ID.

In step S1230, the MCE may transmit a session control message to an eNBbelonging to the determined MBSFN area. The session control message maybe an MBMS session start request message. The cell ID and the MBMS SAImay be included in an MBMS session start request message transmitted bythe MME. The session control message may be an MBMS session updaterequest message. The cell ID and the MBMS SAI may be included in theMBMS session update request message transmitted by the MME. The eNB maybe a road side unit (RSU).

FIG. 13 is a block diagram showing a method in which an MCE controls asession for transmitting a V2X message according to an embodiment of thepresent invention.

Referring to FIG. 13, in step S1310, the MCE may receive from a mobilitymanagement entity (MME) a session control message including a cell listand a source cell indication. The source cell indication may indicate acell in which the V2X message is transmitted. The session controlmessage may be one of an MBMS session start request message and an MBMSsession update request message.

In step S1320, the MCE may filter the session control message on thebasis of the cell list and the source cell indicator.

In step S1330, the MCE may transmit the filtered session control messageto the eNB.

The filtered session control message may include a list of cells managedby the eNB. The eNB may be an eNB for managing a cell indicated by thesource cell indication. Alternatively, the eNB may be an eNB formanaging a neighbor cell of the cell indicated by the source cellindication. The eNB may be a road side unit (RSU).

FIG. 14 is a block diagram illustrating a wireless communication systemaccording to the embodiment of the present invention.

A BS 1400 includes a processor 1401, a memory 1402, and a transceiver1403. The memory 1402 is connected to the processor 1401, and storesvarious information for driving the processor 1401. The transceiver 1403is connected to the processor 1401, and transmits and/or receives radiosignals. The processor 1401 implements proposed functions, processesand/or methods. In the above embodiment, an operation of the BS may beimplemented by the processor 1401.

An MCE 1410 includes a processor 1411, a memory 1412, and a transceiver1413. The memory 1412 is connected to the processor 1411, and storesvarious information for driving the processor 1411. The transceiver 1413is connected to the processor 1411, and transmits and/or receives radiosignals. The processor 1411 implements proposed functions, processesand/or methods. In the above embodiment, an operation of the MCE may beimplemented by the processor 1411.

An MME 1420 includes a processor 1421, a memory 1422, and a transceiver1423. The memory 1422 is connected to the processor 1421, and storesvarious information for driving the processor 1421. The transceiver 1423is connected to the processor 1421, and transmits and/or receives radiosignals. The processor 1421 implements proposed functions, processesand/or methods. In the above embodiment, an operation of the MME may beimplemented by the processor 1421.

The processor may include an application-specific integrated circuit(ASIC), a separate chipset, a logic circuit, and/or a data processingunit. The memory may include a read-only memory (ROM), a random accessmemory (RAM), a flash memory, a memory card, a storage medium, and/orother equivalent storage devices. The transceiver may include abase-band circuit for processing a wireless signal. When the embodimentis implemented in software, the aforementioned methods can beimplemented with a module (i.e., process, function, etc.) for performingthe aforementioned functions. The module may be stored in the memory andmay be performed by the processor. The memory may be located inside oroutside the processor, and may be coupled to the processor by usingvarious well-known means.

Various methods based on the present specification have been describedby referring to drawings and reference numerals given in the drawings onthe basis of the aforementioned examples. Although each method describesmultiple steps or blocks in a specific order for convenience ofexplanation, the invention disclosed in the claims is not limited to theorder of the steps or blocks, and each step or block can be implementedin a different order, or can be performed simultaneously with othersteps or blocks. In addition, those ordinarily skilled in the art canknow that the invention is not limited to each of the steps or blocks,and at least one different step can be added or deleted withoutdeparting from the scope and spirit of the invention.

The aforementioned embodiment includes various examples. It should benoted that those ordinarily skilled in the art know that all possiblecombinations of examples cannot be explained, and also know that variouscombinations can be derived from the technique of the presentspecification. Therefore, the protection scope of the invention shouldbe determined by combining various examples described in the detailedexplanation, without departing from the scope of the following claims.

What is claimed is:
 1. A method of controlling a session fortransmitting a V2X message by a multi-cell coordination entity (MCE) ina wireless communication system, the method comprising: receiving a cellID and a multimedia broadcast multicast service (MBMS) service areaidentity (SAI) from a mobility management entity (MME); determining amulticast broadcast single frequency network (MBSFN) area where the V2Xmessage is to be transferred on the basis of the cell ID; andtransmitting a session control message to a base station which belongsto the determined MBSFN area, wherein the cell ID is an ID of a cell inwhich the V2X message is transmitted.
 2. The method of claim 1, whereinthe MBMS SAI is set to
 0. 3. The method of claim 1, wherein the sessioncontrol message is an MBMS session start request message.
 4. The methodof claim 3, wherein the cell ID and the MBMS SAI are included in theMBMS session start request message transmitted by the MME.
 5. The methodof claim 1, wherein the session control message is an MBMS sessionupdate request message.
 6. The method of claim 5, wherein the cell IDand the MBMS SAI are included in the MBMS session update request messagetransmitted by the MME.
 7. The method of claim 1, wherein the basestation is a road side unit (RSU).
 8. A method of controlling a sessionfor transmitting a V2X message by a multi-cell coordination entity (MCE)in a wireless communication system, the method comprising: receiving asession control message comprising a cell list and a source cellindication from a mobility management entity (MME); filtering thesession control message on the basis of the cell list and the sourcecell indication; and transmitting the filtered session control messageto a base station, wherein the source cell indication indicates a cellin which the V2X message is transmitted.
 9. The method of claim 8,wherein the filtered session control message comprises a list of cellsmanaged by the base station.
 10. The method of claim 8, wherein the basestation is a base station which manages a cell indicated by the sourcecell indication.
 11. The method of claim 8, wherein the base station isa base station which manages a neighbor cell of a cell indicated by thesource cell indication.
 12. The method of claim 8, wherein the sessioncontrol message is any one of an MBMS session start request message andan MBMS session update request message.
 13. The method of claim 8,wherein the base station is a road side unit (RSU).
 14. A multi-cellcoordination entity (MCE) for controlling a session for transmitting aV2X message in a wireless communication system, the MCE comprising: amemory; a transceiver; and a processor for coupling the memory and thetransceiver, wherein the processor is configured to: control thetransceiver to receive a cell ID and a multimedia broadcast multicastservice (MBMS) service area identity (SAI) from a mobility managemententity (MME); determine a multicast broadcast single frequency network(MBSFN) area where the V2X message is to be transferred on the basis ofthe cell ID; and control the transceiver to transmit a session controlmessage to a base station which belongs to the determined MBSFN area,wherein the cell ID is an ID of a cell in which the V2X message istransmitted.
 15. The MCE of claim 14, wherein the MBMS SAI is set to 0.